It took a while for Packer to tune into such dramas. When he first visited the Serengeti lions in 1974, he concluded that “lions were really boring.” The laziest of all the cats, they were usually collapsed in a stupor, as if they had just run a marathon, when in reality they hadn’t moved a muscle in 12 hours. Packer had been working under Jane Goodall in Tanzania’s Gombe Stream National Park, observing baboons. He slept in a metal structure called The Cage to be closer to the animals. In 1978, when Packer’s plan to study Japanese monkeys fell through, he and a fellow primatologist, Anne Pusey, to whom he was married at the time, volunteered to take over the Lion Project, begun 12 years earlier by the American naturalist George Schaller.

By the time Packer and Pusey installed themselves in the Lion House, scientists were well aware that lions are ambush predators with little stamina and that they gorge at a kill, each one downing up to 70 pounds in a sitting. (Lions eat, in addition to antelope and wildebeest, crocodiles, pythons, fur seals, baboons, hippopotamuses, porcupines and ostrich eggs.) Lion territories are quite large—15 square miles on the low end, ranging up to nearly 400—and are passed down through generations of females. Lions are vigorous when it comes to reproduction; Schaller observed one male mate 157 times in 55 hours.

Packer and Pusey set out not just to document lion behavior but to explain how it had evolved. “What we wanted to do was figure out why they did some of these things,” Packer says. “Why did they raise their cubs together? Did they really hunt cooperatively?”

They kept tabs on two dozen prides in minute detail, photographing each animal and naming new cubs. They noted where the lions congregated, who was eating how much of what, who had mated, who was wounded, who survived and who died. They described interactions at kills. It was slow going, even after they put radio collars on several lions in 1984. Packer was always more troubled by the lions’ sloth than their slavering jaws. Following prides at night—the animals are largely nocturnal—he sometimes thought he would go mad. “I read Tolstoy, I read Proust,” he says. “All the Russians.” Packer and Pusey wrote in one article that “to the list of inert noble gases, including krypton, argon and neon, we would add lion.”

Still, they began to see how prides functioned. Members of a large pride didn’t get any more to eat than a lone hunter, mostly because a solitary animal got the proverbial lion’s share. Yet lions band together without fail to confront and sometimes kill intruders. Larger groups thus monopolize the premier savanna real estate—usually around the confluence of rivers, where prey animals come to drink—while smaller prides are pushed to the margins.

Even the crèche, or communal nursery that is the social core of every pride, is shaped by violence, Packer says. He and Pusey realized this after scrutinizing groups of nursing mothers for countless hours. A lactating female nursed another’s young rarely, usually after an unrelated cub sneaked onto her nipple. An alert lioness reserves her milk for her own offspring. In contrast to the widespread belief that crèches were maternal utopias, Packer and Pusey found that nursing mothers stick together chiefly for defense. During takeovers by outside males, solitary females lost litter after litter, while cooperating lionesses stood a better chance of protecting their cubs and fending off males, which can outweigh females by as much as 50 percent.

Surviving cubs go on to perpetuate the bloody cycle. Juvenile females often join forces with their mother’s pride to defend the home turf. Males reared together typically form a coalition around age 2 or 3 and set out to conquer prides of their own. (Hard-living males rarely live past age 12; females can reach their late teens.) A lone male without a brother or cousin will often team up with another singleton; if he doesn’t, he is doomed to an isolated life. A group of lions will count its neighbors’ roars at night to estimate their numbers and determine if the time is right for an attack. The central insight of Packer’s career is this: lions evolved to dominate the savanna, not to share it.

As we crossed the plains one morning, the Land Rover—broken speedometer, no seat belts, cracked side mirrors, a fire extinguisher and a roll of toilet paper on the dashboard—creaked like an aged vessel in high seas. We plowed through oceans of grasses, mostly brown but also mint green, salmon pink and, in the distance, lavender; the lions we hunted were a liquid flicker, a current within a current. The landscape on this day did not look inviting. Sections of the giant sky were shaded with rain. Zebra jaws and picked-clean impala skulls littered the ground. Bones don’t last long here, though; hyenas eat them.

Packer and a research assistant, Ingela Jansson, were listening through headphones for the ping-ping-ping radio signal of collared lions. Jansson, driving, spotted a pride on the other side of a dry gully: six or seven lions sitting slack-jawed in the shade. Neither she nor Packer recognized them. Jansson had a feeling they might be a new group. “They may never have seen a car before,” she whispered.

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